/Engine/Source/Runtime/Landscape/Public/LandscapeEditorServices.h
Attempts to find an edit layer named InEditLayerName in InTargetLandscape. Creates the layer if it does not exist.
The index at which the edit layer named InEditLayerName exists
int32 GetOrCreateEditLayer ( [FName](API\Runtime\Core\UObject\FName) InEditLayerName, [ALandscape](API\Runtime\Landscape\ALandscape) * InTargetLandscape )